1. Field
An aspect of the present invention relates to an electrode catalyst for a fuel cell, and a membrane-electrode assembly for a fuel cell and a fuel cell system including the same.
2. Description of the Related Technology
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and hydrogen in a hydrocarbon-based material such as methanol, ethanol, natural gas, and the like.
Such a fuel cell is a clean energy source that can replace fossil fuels. The fuel cell includes a stack composed of unit cells, and has an advantage of producing various ranges of power. Since fuel cells have four to ten times higher energy density than a small lithium battery, fuel cells have been high-lighted as a small portable power source.
Typical examples of fuel cells are polymer electrolyte membrane fuel cells (PEMFC) and direct oxidation fuel cells (DOFC). A direct oxidation fuel cell that uses methanol as a fuel is called a direct methanol fuel cell (DMFC).
The polymer electrolyte fuel cell has an advantage of having high energy density and power, but also has the problems of requiring careful handling of the hydrogen gas and requiring accessory facilities such as a fuel reforming processor for reforming a fuel gas such as methane, methanol, and natural gas, in order to produce hydrogen.
On the contrary, the direct oxidation fuel cell has a lower energy density than that of the polymer electrolyte fuel cell, but has the advantage of easy handling of a liquid-type fuel, a low operation temperature, and no requirement for additional fuel reforming processors.
In the above fuel cell, the stack that actually generates electricity includes several to scores of unit cells stacked in multiple layers, and each unit cell is made up of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (referred to as a fuel electrode or an oxidation electrode) and a cathode (referred to as an air electrode or a reduction electrode) attached to each other with an electrolyte membrane therebetween.
A fuel is supplied to an anode and adsorbed on catalysts of the anode, and then the fuel is oxidized to produce protons and electrons. The electrons are transferred into a cathode via an external circuit, and the protons are transferred into the cathode through the polymer electrolyte membrane. In addition, an oxidant is supplied to the cathode. Then, the oxidant, protons, and electrons are reacted on catalysts of the cathode to produce electricity along with water.